1. Field of Invention
The present invention relates to drilling systems and shafts therefore and, more particularly, is directed towards a system with a flexible shaft for drilling holes in the roof of a mine.
2. Description of the Prior Art
In the mining industry, falls of mine roofs account for a large percentage of the fatalities that occur in coal mines. Thus, roof control has been a major safety and production consideration. Roof fall fatalities have been greatly reduced in cases where the mine roof is supported with roof bolts that are inserted into holes which are drilled into the mine roof using a drill that is attached to a rigid shaft. As the holes become progressively deeper, the mine worker adds extension sections to the drill shaft. Such an operation requires the worker to be at the head of a roof drilling machine for starting the hole, for adding sections and for inserting the bolts.
U.S. Pat. No. 4,057,115 discloses a flexible shaft for a roof drill with a helically wound inner rod of circular cross section and a helically wound outer band of rectangular cross section. The rod and band are disposed coaxially about an inner sleeve. The round surface of the circular rod provides only line contact, whereby the contact between adjacent turns of the rod is minimal. Minimal contact of adjacent turns of the circular rod tends to permit slippage therebetween and limited strength in axial compression. Due to the foregoing, flat band on circular rod flexible shafts have been met with varying degrees of success.